import java.util.Scanner;

public class Answer2 {
    // 最小花费爬楼梯
    // https://www.nowcoder.com/practice/9b969a3ec20149e3b870b256ad40844e?tpId=230&tqId=39751&ru=/exam/oj
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        int n=in.nextInt();
        int[] cost=new int[n];
        int[] dp=new int[n+1];
        for(int i=0;i<n;i++){
            cost[i]=in.nextInt();
        }

        for(int i=2;i<=n;i++){
            dp[i]=Math.min(dp[i-1]+cost[i-1],dp[i-2]+cost[i-2]);
        }
        System.out.println(dp[n]);
    }
}
